This invention relates to a mechanism for preventing the piston of a disc brake from turning or rolling.
In the conventional disc brakes or the like of the type having friction pads arranged to be pressed against a rotor with the rotating force of a screw shaft which is rotated by an external force converted into an axial forward moving force of a piston which is in screwed engagement with the screw shaft, the position of screwed engagement between the screw shaft and the piston is arranged to be relatively variable to absorb thereby an increase in the gap which increases according as the wear of the lining of the friction pad advances for the purpose of adequately relocating the return position of the piston at the time of brake release.
Meanwhile it is considered essential for the structural arrangement of a disc brake of this type to restrict rolling or turning of the piston round its axis. For this purpose, there have been proposed various contrivances which include, for example, (a) to form the piston into a non-circular shape; (b) to provide turn-preventing projection-and-recess fitting engagement between the piston and the friction pad which is generally unrotatably supported by a support; and (c) in the above stated instance, a load distirbution plate is additionally interposed in between the piston and the firction pad with the two unrotatably engaged with each other.
However, these prior art methods have the following shortcomings: The method (a) is difficult to carry out in terms of machining. In the case of the methods (b) and (c), the load distribution plate tends to be left behind unretracted during the return stroke of the piston to give an adverse effect on rotor rotation, besides the turn preventing arrangement for the piston becomes complicated.